In general, an image forming apparatus is available as a printer, a facsimile machine, a copier, a plotter, or a multi-functional apparatus having multiple functions thereof. Such image forming apparatus may include a liquid dispensing unit having a liquid dispensing head (or a recording head) for dispensing droplets of recording liquid onto a recording sheet to form an image on the recording sheet.
Such sheet includes, but is not limited to, a medium made of material such as paper, string, fiber, cloth, leather, metal, plastic, glass, timber, and ceramic, for example. Further, the term “image formation” used herein refers to providing, recording, printing, or imaging an image, a letter, a figure, or a pattern to a sheet. Moreover, the term “liquid” used herein is not limited to recording liquid or ink but includes anything discharged in fluid form. Hereinafter, the recording liquid is referred to as ink for simplicity of description.
Furthermore, a liquid dispensing unit having a liquid dispenser head can be used in any application area, including, but not limited to, forming an image on a sheet, dispensing liquid for specific purposes (e.g., fabrication of semiconductor), and the like.
Such liquid dispensing unit or image forming apparatus have found industrial applications in such fields as cloth-printing apparatuses and metal wiring devices, while commercial demand for better image quality and faster printing speed continues to grow.
In view of such demand for better image quality, nozzle density, or a number of nozzles per unit area of the liquid dispenser head, continues to increase, narrowing spacing between pressure chambers of a recording head and increasing an energy frequency, or number of vibrations applied to the recording head.
Further, in view of such demand for faster printing speed, a line printer having page-wide arrays (PWA) of recording head has been developed. The main advantage of such PWA head is that it has a length sufficient to print a single line image on a recording medium with a single liquid discharge. However, a drawback of such PWA head is that its manufacture requires consistently high precision to very narrow tolerances.
In general, a recording head or liquid dispenser head includes a nozzle, a liquid chamber communicated to the nozzle, and a pressure generation device to generate pressure for discharging liquid droplets from the nozzle, and a common chamber for supplying liquid to the liquid chamber.
In general, a recording head or liquid dispenser head includes a nozzle, a liquid chamber that communicates with the nozzle, and a pressure generator to generate pressure for discharging liquid droplets from the nozzle.
Such recording head may use known methods for discharging liquid droplets, such as a thermal method, a piezoelectric method, and an electrostatic method. In the thermal method, an electricity-heat conversion element such as a heating resistor is used to cause a film boiling of liquid. In the piezoelectric method, an electricity-mechanical energy conversion element such as a piezoelectric element is used. In the electrostatic method, an electrostatic actuator, which generates electrostatic force, is used.
In such image forming apparatus, an image having higher quality can be produced by enhancing a responsiveness of the pressure chamber with respect to energy (e.g., pressure) applied to the pressure chamber.
Specifically, if a resonance cycle of the pressure chamber can be set shorter, the pressure chamber may response to energy (e.g., pressure) applied to the pressure chamber more efficiently and effectively.
For example, such resonance cycle of the pressure chamber can be set shorter by reducing a size (or volume) of the pressure chamber. However, if the size (or volume) of the pressure chamber is reduced, liquid volume that can be dispensed by a single dispensing operation becomes smaller, which is not preferable for producing an image having higher quality.
If liquid volume dispensed by a single dispensing operation becomes smaller, an amount of liquid droplets, which is required for forming an image having higher quality, may be jetted by increasing a number of nozzles (or density of nozzles) of the recording head or by increasing scanning movement of the recording head in case of a serial image forming process. However, such modification to an image forming process may result into complicated manufacturing processes of a recording head, or decreased productivity (e.g., decreased print speed) due to increased number of scanning movement of the recording head.
Alternatively, in some related arts, a resonance cycle of a pressure chamber may be set shorter by increasing rigidity or stiffness of parts configuring a pressure chamber of a recording head.
In this disclosure, rigidity or stiffness of parts configuring the pressure chamber may be referred with a term of “compliance”. In general, “compliance” indicates a volume change of an object (e.g., parts configuring a pressure chamber) per unit pressure applied to the object, and the compliance inversely relates to rigidity or stiffness of the object.
For example, if one object has a lower compliance value, the object has a greater stiffness, which means the object is relatively hard to change its volume when a pressure is applied to the object. On the other hand, if one object has a greater compliance value, the object has a lower stiffness, which means the object is relatively easy to change its volume when a pressure is applied to the object.
Accordingly, in case of related arts, if compliance of parts configuring a pressure chamber can be set to a smaller value, a stiffness of the pressure chamber can be increased, by which a resonance cycle of the pressure chamber can be set shorter.
Generally, background arts have a configuration, which may increase a stiffness of a pressure chamber so that a resonance cycle of the pressure chamber can be set shorter. In other words, compliance of a pressure chamber may have a smaller value in background arts.
In one related art, a structural compliance of parts configuring a pressure chamber is set smaller than a compression compliance of a recording agent (e.g., ink) used for the pressure chamber, wherein the structural compliance indicates a volume change rate of parts configuring the pressure chamber per unit pressure applied, and the compression compliance indicates a volume change rate of the recording agent per unit pressure applied.
By setting the structural compliance of parts configuring the pressure chamber smaller than the compression compliance of the recording agent, a stiffness of the pressure chamber may be increased, by which a resonance cycle of the pressure chamber can be set shorter.
Further, in another related art, a vibration plate, used to apply a pressure to a pressure chamber, may be configured with a plurality of layers (e.g., three layers), in which one layer has a higher rigidity (or smaller compliance) and another layer has a lower rigidity (or greater compliance). The vibration plate may have such configuration so that a layer having smaller rigidity can vibrate by a pressure energy applied to the pressure chamber and a layer having greater rigidity may contribute to set a resonance cycle of the pressure chamber to a shorter time.
Furthermore, in another related art, a compliance of ink “C1” and a compliance of vibration plate “C2” used for a pressure chamber may have a compliance ratio of C2/C1, ranging from 5.4 to 10, for example.
Although the rigidity of a pressure chamber may be increased with above-mentioned methods, such methods may have some drawbacks for a viewpoint of configuration of the pressure chamber.
In general, a pressure chamber may be configured with a metal material having higher rigidity (e.g., Si, SUS, Ni) and a vibration plate, which becomes a wall face of the pressure chamber, wherein the vibration plate has an energy-transmitting area (or portion) for transmitting pressure energy, generated by a pressure generator, to the pressure chamber. Because such energy-transmitting area (or portion) of the vibration plate may need to have a lower rigidity for effectively vibrating and transmitting pressure energy to the pressure chamber, such energy-transmitting area of the pressure chamber may not be set to a greater rigidity. Accordingly, the rigidity of the pressure chamber as a whole may not be increased so easily.
Further, if a rigidity of the pressure chamber as a whole may be set to a lower level by setting a structural compliance of parts configuring a pressure chamber smaller than a compression compliance of a recording agent (e.g., liquid) as above mentioned, a compliance of the pressure chamber as a whole may become greater. In other words, the rigidity of the pressure chamber as a whole may become smaller, which may result into a longer resonance cycle of the pressure chamber, which is not preferable for producing an image having higher quality.
Further, although the rigidity of a pressure chamber as a whole can be set greater by using a vibration plate configured with a plurality of layers as above mentioned, such vibration plate may need a complicated or time consuming manufacture process, or such vibration plate may cause to restrict a structural design of a recording head, which is not preferable from a view point of manufacturing cost or design works of a recording head.